potty mouth

Emotional First Aidを読んでいます。
Scientists have investigated several such "will power workouts," including focusing on our posture (great for slouchers); avoiding cursing (more effective for potty mouths than it is for the "gosh darn it!" set); avoiding sweets, cookies, or cakes (great if you have a sweet tooth); squeezing a handgrip twice a day for as long as we can (handgrips are cheap and can be found in sporting goods sotres); and the one I think works best--using our nondominant hand.
"potty mouths" の意味を辞書で見ます。
・Oxford English Dictionary: Using or characterized by bad language.: a potty-mouthed rapper
・Wiktionary: The characteristic of regularly using vulgar language, especially strong profanities.: Sometimes this noun is used attributively, as, for example, in: The language of my potty-mouth coworkers can be very offensive.
"potty" にオマルの意味があるのが語源かと推測しますが、語源を説明している辞書は見つかりませんでした。